Simulations of Hypertrophic Obstructive Cardiomyopathy (HOCM) in a Human Heart Left Ventricle using ANSYS/CFX/Fluent

Simulations of Hypertrophic Obstructive
Cardiomyopathy (HOCM) in a Human Heart
Left Ventricle using ANSYS/CFX/Fluent
Vladimir Kudriavtsev (Intevac),
Metin Ozen, Can Ozcan
(Ozen Engineering)
1 © 2014 ANSYS, Inc. ANSYS Users Regional Conference, Santa Clara 2014

Considerable Interest Lately: LV, HOCM, Heart
Fluid Structure Interactions

Human Heart Model
Model courtesy of Dr. Jingwen Hu, PhD
University of Michigan Transportation Research Institute
Real Geometry of LV
mm
MITRAL
AORTIC
LV-left ventricle

Schematic diagram of a patient with a normal heart (left) and
a patient with hypertrophic cardiomyopathy (right).
Nishimura R A et al. Circulation. 2003;108:e133-e135
Copyright © American Heart Association, Inc. All rights reserved.
Wall thickening
Septal subaortic
bulge, Flow
obstruction
Mechanism of dynamic outflow tract
obstruction. The upper schematic shows a
representation of the mitral leaflets. The
elongated mitral leaflets that are drawn into the
Left Ventricular Outflow Tract during early
systole with midsystolic prolonged systolic
anterior motion- septal contact, malcoaptation
of the mitral leaflets, and the resultant
posteriorly directed jet of mitral regurgitation.

Simulated 3D LV Geometry –
fully parametric
in Design Modeler
Imposed wall motion
Parametric Geometry Definition

Typical Heart Left Ventricle LV
Dimensions
http://www.echopedia.org/wiki/Normal_Value
s_of_TTE#Left_Ventricle

CFX Model Definition
Inlet pressure is prescribed as
sin or cos time dependent
wave, which is always positive
Wall Motion is Prescribed
as sin time dependent in
Radial and Axial

Oscillating CFX-ANSYS 2-way FSI
Tutorial CFX, P=600Pa
Fails, when “angle” <90 deg
We increase boundary pressure up to 600Pa. Tutorial Fails,
negative mesh volume P>680Pa
“angle”

Valve Hyper-elastic Transient Simulations
Moonley-Rivlin Model;
Pressure extrapolation from
Transient Simulation. Requires
multiple and small time steps
Valve Initial Position
Valve fully open

First CFX-ANSYS 2Way FSI Results:
Flow Valve Interactions
Coupled flow simulation fails due to negative mesh
when valve deformation
significant
Hyper-elastic valve model (stand alone)
with external pressure allows significant
deformation, when not coupled with CFX

Example of Systolic-Diastolic Transient
Flow in Left Ventricle (CFX)
Moving Wall to simulate displacement and ejection effect during
systole and volume filling effect during diastole
No Valves, blocking flow effect of valves is simulated using transient
(sin or cos) pressure pulse at Mitral Inlet and CFX Outflow Boundary
condition (does not allow backflow) for Aortic Valve
Stroke Volume, displacement volume
and pressure magnitude , heart rate
are matched
Example of Steady State Simulation,
Clearly grossly inadequate for the mechanics
involved

Mass Flow – Mitral and Aortic
Re=5281
Aortic Outflow
Positive—
Mitral inflow
Negative-
Aortic outflow
Mitral inflow
Zero—Mitral
inflow during
systolic
contraction
Close to zero
during
diastolic
expansion.

Diastolic Phase
CFX4 CFX14

Beginning of Systolic Contraction
CFX22
CFX18
End of Diastolic
Wall motion

Systolic –flow squeeze action
Wall motion
Recirculations are
getting suppressed
CFX23 CFX29
No mitral
outflow
No mitral
outflow

End of Systolic Phase
No recirculations are left due to flow squeeze action
CFX31 CFX34
No mitral
Aortic outflow Aortic outflow outflow

Transient 2-way FSI Valve Motion
Simulation with Remeshing (FLUENT, 2D)
Small Septum Hump
Larger Septum Hump, valve is
entrained closer to septum wall
NO WALL MOTION
No Aortic Valve/No
aortic outflow
blockage
diastolic

Obstruction Mechanism
Septum Hump
Systolic
wall
motion
direction
Systolic
wall
motion
direction
From this moment and on as LV wall and
septum move towards each other during
systole (creating ejection into aortic valve)
MITRAL leaflet that is already deflected and
obstructing diastolic flow with Venturi
effect of lower pressure behind it only gets
pushed further by mechanical forces and
fluid forces to do more obstruction as lower
pressure zone behind it fails to create
enough lateral push

Obstruction Mechanism
Systolic
wall
motion
direction
Systolic
wall
motion
direction
Venturi effect of lower pressure behind it
only gets pushed further by mechanical
forces and fluid forces to do more
obstruction as lower pressure zone behind
it fails to create enough lateral push
Systolic
wall
motion
direction

Moving Wall and Systolic Engagement
Valve: E= 2.5MPa, v=0.33
Inlet and wall conditions are copy/paste from your simulation setup.
Inlet condition: 2000 Pa * abs(sin(t*3.85))
Wall Movement: 0.005*abs(sin(t*3.85)) or 0.015*abs(sin(t*3.85))
Recirculation
pushed
toward hump
and aorta
End of diastolic flow obstruction
(valve laterally deflected)
Recirculation
formed

Systolic Obstruction and Lateral
Entrainment of Mitral Leaflet Systolic flow obstruction
Recirculation
blocks aortic
outflow,
Creates low
pressure
zone
Entrains
valve
laterally into
Obstructive
position as
wall is
moving
inward

Obstruction Mechanism -2
Towards the end of systole, insteadof being
pushed away into normal position, leaflet is
entrained laterally right into the aortic exit
path – thus blocking outflow and this
positioning is stable. No forces at play to
return it back to normal.
Systolic
wall
motion
direction
Septum Hump

Echocardiographic results - HOCM
Flapping and flow obstruction
during ejection (systole)
Both valves closed
Hump Touchdown during
expansion (diastole)
End of diastole and Aortic
valve closed
Aortic opened, mitral closed
Mitral opened, aortic closed

Summary of Work -1
-Studied LV geometries and more detailed models, developed
simplified parametric transient 3D model with moving walls
using CFX;
-Studied “2 way FSI” Capabilities of ANSYS/CFX for moving
elastic valve of fixed thickness [oscillating.* Tutorial]. Found
limitations of method when large deformation are involved due
to negative grid and deficiencies of grid interpolation in CFX;
-Studied separate valve motion transient analysis with hyper-elastic
valve material model and extrapolated pressure loads
from transient CFX flow model. Demonstrated capability to
simulate transient valve motion in the solid ANSYS module;

Summary of Work -2
-Coupled valve motion with transient flow in moving
ANSYS/CFX, failed interpolated meshes due to inability to re-mesh;
-Used Fluent/ANSYS 2-way FSI with re-meshing to study
deforming valve problem in 2D;
-demonstrated interaction of 2D moving valve with moving
mesh for simulations with hump and without hump on wall
septum.
-demonstrated mechanism of mitral valve flow obstruction for
HOCM.
Next steps: conduct similar analysis in 3D or find way to solve
in ANSYS /CFX environment (try shell models with no thickness
for valve to ease mesh interpolation)

Simulations of Hypertrophic Obstructive Cardiomyopathy (HOCM) in a Human Heart Left Ventricle using ANSYS/CFX/Fluent

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